As disclosed in copending application Ser. No. 625,885 various types of communications techniques are employed in order to enhance the security of information being transmitted between a base or ground station and a remote station or vehicle, such as a pilotless reconnaissance aircraft, and to make such communications more resistant to intentional jamming or noise.
In the aforementioned copending application there is described a method and apparatus for preventing intentional jamming of a transmitter and receiver in a secure communications system of the frequency-hopping type wherein an information signal is generated at the transmitter, the information signal including at least a portion representative of the frequency of transmission of the next information signal. The information signal is then transmitted and received at a remote receiver at a frequency determined by the frequency representative portion of an immediately preceding transmitted information signal.
While the system described in this copending application is adequate where there is to be direct communication between a transmitter and a receiver, a need may arise for a base station to communicate with multiple remote units through a relay unit.